Sunbeams flicker through the translucent young foliage of the sycamore canopy overhead. A shadow darts among them: a blackcap, pecking aphids from the underside of the leaves.
The insects hatched from overwintering eggs in early April, congregating on loosening bud scales, waiting for tender new leaves to unfurl. Now there are legions of them, aligned along leaf veins, hypodermic stylets plugged in, siphoning sweet sap while simultaneously giving birth to more. They stand with regimented parade-ground spacing, just close enough to stay in touch with their long antennae. A shiver of fidgeting sweeps through the colony as the blackcap approaches.
Conservationists are quick to point out that sycamore sits close to the bottom of an oft-quoted league table of diversity of insect species hosted by trees, but there is an alternative measure of the tree’s value. That superabundance of a single aphid species contributes to a food web of warblers, tits, hirundines and predatory insects. It’s an ecosystem asset. A 20-metre specimen can host an estimated 2.5 million aphids, diverting its photosynthetic energy into fuelling their own exponential reproductive potential. They in turn fall prey to hoverfly larvae, ladybirds and lacewings. In summer, the winged adults join the aerial plankton hunted by swallows, house martins and swifts. Survivors will lay overwintering eggs in leaf buds, ready for next spring’s population explosion.
Sycamore, non-native and invasive, is perhaps our least-loved deciduous tree. As long ago as 1664, John Evelyn, in his Sylva, a treatise on Britain’s trees, despised sycamore for its “honey-dew leaves, which fall … and mar our walks”, and wanted to see it “banished from gardens and avenues”. Motorists might concur if they park in its shade and find cars covered in a sticky film of honeydew, excess tree sap that falls in a constant rain from aphid anuses after they’ve extracted nutrients they need.
And yet, for all the species’ purported faults, the felling of the famous Sycamore Gap specimen, a landmark on Hadrian’s Wall familiar to generations of walkers, provoked an outpouring of public grief and outrage. Sentiment, as well as science, has a powerful influence on attitudes to our flora and fauna.
• Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 15% discount
